1. Technical Field
The present invention relates generally to an improved data processing system and in particular to a method and apparatus for accessing data on a storage device. Still more particularly, the present invention relates to a method and apparatus for accessing data on storage media in the form of a tape.
2. Description of Related Art
Tape drives also are peripheral mass storage devices often used to archive data on tapes for later access. Tape drives are also used as random access devices in data storage applications where cost of storage might be important and access time is of less significance. For example, many banks and financial institutions, insurance companies, and government agencies may use tape drives with applications regarding clients, accounts, patients, and other items of interest. In other applications, huge amounts of data are stored directly on tape for later retrieval and analysis. For example, with geophysical and space exploration, information gathered may be stored and analyzed at a later time. Today, much of the tape is stored in automatic libraries or silos in which the tapes are handled by robots. The tapes in these systems are automatically inserted into attached arrays of tape transports. These libraries are depositories of data cartridges and come in many sizes from tens of cartridges to as many as 6,000 cartridges within a single unit. Tape drives are commonly available in a cartridge format to archive data and software and to transport data and software between different computer systems. Further, tape also is used to back up critical data in case of a failure of the primary storage device, such as a hard disk drive.
In accessing data on a tape, a read or write head in a tape drive is positioned over one or more tracks on the tape. A servo track may be used for aligning the read or write head to the tracks containing the data. If the read or write head drifts from an optimal position relative to the track on the tape, an error signal is generated. The error signal increases as the read or write head drifts further from the optimal location relative to the data on the track on the tape. If the read or write head drifts too far relative to the data on the track, errors and data recovery problems occur in accessing the tape. Presently available systems adjust the position of the read or write head or the position of the tape relative to the read or write head to minimize the error signal generated during access of the tape.
Tapes often include a number of servo tracks with which transducers in a read or write head must stay aligned. The present invention recognizes that the alignment mechanisms used to move a tape or a read or write head to line up with a servo track are unable to efficiently compensate for changes in distance between these tracks when the width of the tape changes. As track densities increase, these variations in tape width may cause head transducer-to-tape track misalignments resulting in data errors.
Therefore, it would be advantageous to have an improved method and apparatus for minimizing tape width dimensional changes.
The present invention provides a method and apparatus for reducing tape dimensional changes during accessing of a tape. A profile for the tape is identified. A determination is then made as to a location that is being accessed on the tape. Tension applied to the tape is adjusted using the location and the profile, wherein tape width dimensional changes are minimized. Also, the tape width dimensional changes in the tape may be detected while the tape is being accessed. In this case, a signal is generated to alter the tension applied to the tape to minimize tape width dimensional changes.